Effect of metal layer stacking order on the growth of Cu2ZnSnS4thin films

Abstract

In this paper we have presented an in-depth study of effect of metallic precursor stacking order on the growth of the Cu2ZnSnS4 (CZTS) thin films. The CZTS films were prepared by employing a two-step process comprising of sequential sputtering of the metal precursors followed by sulfurization. An optimized stacking sequence as well as growth mechanism for obtaining the single phase CZTS has been proposed based on the results of XRD, Raman, XPS, UV–Vis and electrical studies. A combination of Raman analysis and XPS has been carried out to confirm the CZTS phase formation and to detect any minor phases, if present. The occurrence of Raman modes at around 286 and 336cm−1 for the Zn/Cu/Sn/Cu stack sulfurized at 500°C indicated the existence of prominent Kesterite CZTS phase. The perfect homogeneous mixing of sequential precursors together with the elemental sulfur was observed in the case of sulfurized stack order of Zn/Cu/Sn/Cu, which yielded single phase CZTS films, and further confirmed by high resolution core level XPS measurements. Stack dependent micro structural features and elemental analysis were also carried out using FESEM attached to EDS. The p-type charge carriers as detected using hot-probe measurement technique and the band-gap energy of ∼1.52eV as estimated from the absorbance spectrum, suggested that the Zn/Cu/Sn/Cu stack order is most appropriate for realizing single phase CZTS growth using two step method.